Musk begged his friend for forgiveness after learning of Brin's divorce from him.
According to sources close to the matter, Brin acknowledged the apology, but the two tech moguls are not currently talking.
According to the Journal, Musk's affair with Brin's wife began at the Art Basel art show in Miami in December. Brin and Shanahan were separated at the time, but still living together, and faced difficulties caring for their toddler daughter, according to sources.
Brin filed for divorce in January. Sources said Brin told his advisers to sell his investments in Musk's businesses because of his strained relationship with Musk. Brin invested half a million dollars in the company in 2008.
I hope we can move forward with honesty and harmony for the sake of our child. "We are working towards that, and we are both doing that."
When Musk broke up with his girlfriend, he was accused of having an affair. A daughter who was born via surrogate the same month as the affair took place is one of the two children. Insider's Julia Black said that Musk had twins with one of his top executives.
The news comes at a time when Musk is facing a number of public professional challenges, including a legal battle with the social media platform.